Much has been done in the last few years to provide sophisticated springing in upholstered furniture. The inventions disclosed in U.S. Pat. Nos. 3,210,064, 3,388,904 and 3,525,514, as well as others assigned to the same assignee as the present invention, achieve high levels of comfort and luxury in full-upholstered furniture of the type which permits a high-arc profile for the seat springs. They achieve the same ends in full-upholstered furniture which, when loose cushion, uses the popular, single, thinner, flat profile, poly-foam non-wrapped cushions. Such furniture is largely tight-back rather than loose (pillow)-back. It is often tight-seat rather than loose (cushion) seat, also.
In recent years there has been an industry trend towards very thick (6"-7" or more), multi-layered, poly-foam wrapped cushions having a pronounced high-curve profile. There has also been a trend toward loose-pillow-backs; toward loose-cushion (hard-edge or spring-edge) seats and toward high-style "motion" furniture.
Such trends have created new problems. These include cushion-gap; less frame pitch, resulting in less room for comfort contributing features; less cushion-base pitch and cushion pitch; a need for the same comfort in hard-edge, loose cushion seats as was formerly achieved in spring-edge, loose cushion seats; and a need for increased yield at the front rail to balance "sink-in" at the back rail created by the new, extra-thick cushions.
In the aforedescribed new trend in furniture, internal parameters as well as style requirements make the use of normally high-arc springs (even with the superior seat luxury associated with them) undesirable. This is because of the necessity of maintaining standard heights from floor to cushion top (even with extra-thick cushions); of preventing the opening up of an unsupported area at the lower end of the subject's back when sitting in loose-pillow-back styles; of preventing unsightly cushion-gap at the front end of loose cushion styles; and of providing desired comfort standards in the new, largely loose-cushion, motion-furniture.
Many unsuccessful expedients have been used to ameliorate these conditions. For example, wire grids, half-height continuous coils, or light-gauge, standard-arced springs, pulled down flat enough to meet the installation necessities, have been employed. Unfortunately, they have resulted in hard, inferior seats, whose only yield is in the cushion and not in the spring base (which should be the major source of both yield and upward buoyancy under load).
A solution to these problems has been elusive. A furniture manufacturer has been faced with mutually contradictory factors which create a very difficult environment for comfortable seating. First, the crown of the seat springs relative to the point of suspension or rail attachment must be lower than that of high-arc springs by a substantial factor, ideally from approximately 11/4" to 13/4" as opposed to 21/4 to 23/4" for high-arc springs. Second, relative to high-arc springs and the three most important factors in luxury seating (initial-drop, deep-drop and upward resilience), the solution, in order to meet these requirements, must have increased initial-drop, less deep-drop, and as nearly as possible the same upward resilience. Third, the solution must provide for closing cushion-gap in both spring-edge and hard-edge furniture.